1. Field of the Invention
The present invention relates to an optical connector. The present invention particularly relates to an optical connector and assembling method for the same in which so called a Polarization Maintaining optical fiber is formed so as to be able to butt-connect and stress distribution of the cross section is different in two orthogonal directions.
FIG. 15 shows a conventional optical connector ferrule.
If FIG. 15, an optical connector ferrule 1 is made of ceramic, zirconium, and the like, and an optical connector ferrule 1 is a sleeve through which fine pores 2 are formed along a central axis line. Through the fine pores 2, an optical bare fiber 4 of which cover on the tip of optical fiber 3 (mainly an optical fiber core line) is removed is inserted from a rear end (center-right region in FIG. 15) of butt-connection direction of the optical connector ferrule 1. The rest of the cover 3a of the bare fiber 4 on the optical fiber 3 is fixed in a flange unit 5 having cylindrical shape which is fixed to a rear end of the optical connector ferrule 1 by bonding with bonding agent or the like.
Conventionally, so called a Polarization Maintaining optical fiber which can maintain and transport polarization phase of the transmitted light is provided as an optical fiber which can be used for various sensors and gyrotrons.
There are tow Polarization Maintaining optical fibers such as 1) an optical fiber of which stress distribution in a clad is asymmetric (stress birefringent), and 2) an optical fiber of which refractive index distribution is asymmetric by differentiating a component of the material for a clad partially (structural birefringence). In both Polarization Maintaining optical fibers, polarization can be transmitted stably by giving large birefringence to an optical fiber in advance. As Polarization Maintaining optical fiber such as above type 1), so called a PANDA type polarization Maintaining optical fiber (PANDA: Polarization-Maintaining and absorption-reducing) can be named typically. The PANDA type Polarization Maintaining optical fiber has a stress giving section made of quartz glass to which B2O3 is added for example, and the stress distribution is formed asymmetrically. In the PANDA type Polarization Maintaining optical fiber, even if an optical fiber is bent, unification of polarization mode hardly occurs, and the polarization of the light can be maintained and transmitted as such. When the above type 1) of Polarization Maintaining optical fiber was applied for an optical connector ferrule 1 so as to assemble an optical connector on the tip of this optical fiber, there used to be a concern that required optical property could not obtained because the stress distribution changed. If the above Polarization Maintaining optical fiber is inserted in fine pores 2 which is formed so as to penetrate along the entire length of the optical connector ferrule 1 such as a ferrule for the use of SC type optical connector (SC: Single Coupling optical fiber connector) defined in Japanese Industrial Standard (JIS) C5973, there was a case in which an optical fiber is bent unintentionally due to the difficulty of the inserting operation because the length of the bare optical fiber 4 (particularly a bare optical fiber) of which cover on the tip of the Polarization Maintaining optical fiber was removed is very long. There was also a disadvantage that stress strain occurs between the inner surface of optical connector ferrule 1 and the optical fiber (particularly bare optical fiber); thus, polarization property (extinction ratio) of the Polarization Maintaining optical fiber changes. Also, there is a possibility that the polarization property changes according to temperature due to a difference of coefficient of linear expansion between ferrule material and optical fiber to some extent.
For above reasons, there has been a requirement for developing an optical connector for a Polarization Maintaining optical fiber in which the required optical property can be obtained quite stably.
When Polarization Maintaining optical fibers are butt-connected each other by coupling optical connectors (including connection via an optical connector adapter), for example, in order to maintain and continue the polarization of the transmitted light between the both Polarization Maintaining optical fibers, it is necessary to butt-connect while synchronizing the stress distribution of the both Polarization Maintaining optical fiber accurately by positioning between the both stress giving sections of the Polarization Maintaining optical fibers. As far as an optical connector in which a housing is attached on the outside of the optical connector ferrule is concerned, it is common that the connecting is possible only in a required configuration according to engagement and fitting condition between the housing of the optical connector and the housing of the other optical connector (various female optical connector including optical connector adapter). When the configuration of the housings is fixed, the configuration of the optical connector ferrules which are supported in the housings is also fixed; thus, the configuration of the Polarization Maintaining optical fibers which are inserted and fixed in the optical connector ferrules is fixed. If it is necessary to maintain the polarization of the transmitted light between the both Polarization Maintaining optical fibers, the direction of the Polarization Maintaining optical fiber is positioned towards the housing by each optical connector so that the stress giving sections coincide between the both Polarization Maintaining optical fibers when optical connectors are connected.
Conventionally, it was common that an optical connector ferrule, a flange unit, and an optical connector which is provided with a housing are assembled by attaching the flange unit to the optical connector ferrule and inserting a bare fiber into the optical connector ferrule and further attaching the housing to the flange unit. A space between the housing and the flange unit is positioned by engagement of a key and a key slot. In such an assembling method, it is impossible to adjust the circumferential direction of the optical connector ferrule against the housing after the space between the housing and the flange unit is fixed. Therefore, it is impossible to change a circumferential direction of the Polarization Maintaining optical fiber after the Polarization Maintaining optical fiber is inserted and fixed in the optical fiber ferrule. That is, there used to be a complaints on the optical connector which was assembled by the above assembling method that it is impossible to change or adjust the circumferential direction of the Polarization Maintaining optical fiber which is inserted and fixed in the optical connector ferrule toward the housing because it is impossible to change the attaching direction of the flange unit which is fixed on the optical connector ferrule toward the housing, even if it is required to change the circumferential direction of the Polarization Maintaining optical fiber toward the housing according to the structure of the optical connector to fit with and the adjustment of connecting direction of the Polarization Maintaining optical fiber which is connected by the optical connector.